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That's why President Obama today urged China to do more to restrain North Korea.

Obama met with his Chinese counterpart, Hu Jintao, on the sidelines of a security summit in the South Korean capital, Seoul.

Obama said earlier that China's efforts to influence its Communist ally had been ineffective.

North Korea is preparing to launch a satellite next month, which the US and its allies believe is cover for a long range ballistic missile test.

"It's not the satellite itself that's a concern in the West," says Miles Pomper, an expert with the Monterey Institute's Center for Non-proliferation Studies. "It think it was John F. Kennedy who once said that the only difference between rockets and missiles is attitude."